The production of organic compounds using carbon monoxide or synthesis gas, which is a mixture of carbon monoxide and hydrogen, as reactant has been known for a significant period of time. It is well known that one can produce methanol directly from synthesis gas and that methanol can be further reacted by hydroformylation, homologation and carbonylation reactions to produce acetaldehyde, ethanol and acetic acid or its methyl ester, respectively. It is also know that esters, ethers, and other organic compounds can be reacted with carbon monoxide or synthesis gas to produce oxygenated organic compounds. The difficulties, however, have resided in the ability to carry out any one of these chosen reactions to produce the desired compound at acceptable efficiency, conversion rate and selectivity.
In almost all instances the reaction is generally catalysed using a Group VIII transition metal compound as catalyst and a halogen as the promoter. It is known that many other metal compounds and promoters can be used. In addition, the prior art has disclosed the use of secondary activators or ligands in conjunction with the metal catalysts and promoters. These secondary activators can be other metallic salts or compounds, amines, phosphorus compounds, as well as a multitude of other compounds that have been disclosed in the published literature. Thus, a typical catalyst system contains the metal atom catalyst, promoter and, optionally, ligands, solvents and secondary activators. Though a significant amount of literature does exist describing the production of oxygenated compounds by the isomerisation of methyl formate, to our knowledge it does not disclose or suggest our invention. Several of the pertinent patents in this area are discussed below.
French Patent No. 2,317,269, filed by Compagnie Des Metaux Precieux and published on Feb. 4, 1977, discloses the production of aliphatic carboxylic acids by the reaction of an alcohol with carbon monoxide in the presence of a catalyst containing at least three essential components, iridium atom, copper atom and halogen. This is not our process.
In European Patent Application No. 0018927; filed by Gauthier-Lafaye et al on Apr. 23, 1980 and published on Nov. 12, 1980, there is described a process for the production of monocarboxylic acids by the carbonylation of an alcohol using a nickel catalyst, a halide and a solvent; in this reference synthesis gas is used.
In European Patent Application No. 0045637, filed by Pruett on Jul. 31, 1981 and published on Feb. 10, 1982, there is disclosed the direct conversion of formic acid esters to their corresponding carboxylic acids without the presence of carbon monoxide using as catalyst a soluble iridium salt and an iodine promoter. This is not our catalytic process.
Another known procedure for producing acetic acid is the catalytic isomerisation of methyl formate as shown by the reaction: EQU CH.sub.3 OOCH.fwdarw.CH.sub.3 COOH
This procedure is shown in U.S. Pat. No. 1,697,109, issued to Henry Dreyfus on Jan. 1, 1929. The process described is a vapour phase isomerisation reaction carried out at 200.degree. C. to 450.degree. C. at a pressure up to 200 atmospheres using a metal oxide or acetate catalyst. It does not disclose the use of rhodium and lithium iodide plus optionally methyl iodide or alcohols as starting materials.
U.S. Pat. No. 2,508,513, assigned to Celanese Corporation and issued on May 23, 1950 claims an iron metal atom based catalyst, e.g. nickel, promoted with methyl iodide for the isomerisation of methyl formate to acetic acid, carried out at 300.degree. C. to 400.degree. C. and a pressure up to 400 atmospheres. Carbon monoxide may be present. It does not disclose the use of rhodium and lithium iodide plus methyl iodide nor of alcohols as starting materials.
U.S. Pat. No. 3,060,233, issued to Hohenschutz on Oct. 23, 1962, discloses the carbonylation of methanol to acetic acid using a metal of the iron group of the Periodic Table and a halide. It does not disclose use of rhodium.
U.S. Pat. No. 3,769,329, issued Oct. 30, 1973 to Paulik et al, discloses the production of carboxylic acids from alcohols, or the ester, ether and halide derivatives thereof, and carbon monoxide using a rhodium catalyst and a halogen component. It does not mention lithium iodide or mixtures of lithium iodide and methyl iodide. The process disclosed in this reference requires the use of acidic halogen compounds which are corrosive and difficult to handle. High levels of methyl iodide are used and recycled in order to maintain activity. Further, the preferred mode of operation of this process uses a large excess of water to ensure selectivity to acetic acid.
U.S. Pat. No. 3,798,267, issued Mar. 19, 1974, relates to the conversion of methyl formate to acetic acid in the presence of a catalyst system consisting essentially of activated carbon and a halogen promoter. The reference uses catalyst and starting materials different than those employed in the invention of this application.
U.S. Pat. No. 4,194,056, filed by Antoniades and issued Mar. 18, 1980, discloses the production of carboxylic acid from methyl formate using a soluble rhodium catalyst, halogen promoter and carbon monoxide. This is not the process of the instant invention, nor does this reference suggest or disclose the use of lithium iodide or a mixture of lithium iodide plus methyl iodide and the unexpected results achieved by such use.
U.S. Pat. No. 4,212,989, issued to Isshiki et al on Jul. 15, 1980, describes a process for producing carboxylic acids or their esters by reacting an alcohol or an ether with carbon monoxide using a Group VIII metal catalyst and an iodine promoter. The reference contains no suggestion or disclosure of the production of organic carboxylic acids by the process of our invention.
British Patent Specification 1,286,224, issued Aug. 23, 1972 to Wakamatsu et al, relates to the reaction of methyl formate with carbon monoxide in contact with a rhodium catalyst and a halogen promoter to produce acetic acid. It contains no recognition of the distinct advantages achieved with the use of lithium iodide with or without methyl iodide, in fact it does not mention mixtures of these specific compounds.
British Patent Specification 1,293,193, issued Oct. 18, 1972 to Japan Gas-Chemical Company Inc, relates to the direct conversion of formic acid esters to the corresponding carboxylic acids, in the presence of carbon monoxide, a catalyst that is a Group IIb or VIII metal and an organic polar solvent. It does not disclose use of rhodium atom plus lithium iodide with or without methyl iodide.
Japanese Patent Publication 50-16773, filed by Kuraishi et al and published on Jun. 16, 1975, discloses the production of an organic acid from the corresponding formic acid ester in the presence of carbon monoxide using a catalyst system containing cobalt, iron or mercury and a halogen plus an alkali metal salt of a lower aliphatic carboxylic acid, triamine or cyclic amine.
Japanese Patent Publication 51-65703, filed by Mitsui Petrochemical and published on Jun. 7, 1976, discloses the reaction of methyl formate in the presence of carbon monoxide using a system containing a rhenium catalyst and halogen compound to produce acetic acid.
Japanese Patent Publication 56-22745, filed by Wada et al and published Mar. 3, 1981, discloses the isomerisation of a formic acid ester to the corresponding acid in the presence of carbon monoxide, palladium atom, halogen and base.
Japanese Patent Application No. 56-73040, filed by Isshiki et al and published on Jun. 17, 1981, relates to a process for producing acetic acid by isomerising methyl formate in the presence of carbon monoxide using a nickel catalyst, an iodine compound and an organic nitrogen compound.
Japanese Patent Application 56-83439, filed by Isshiki et al and published Jul. 8, 1981, discloses a method for producing acetic acid by heating methyl formate and carbon monoxide in contact with a catalyst containing palladium, ruthenium and/or iridium metal atom and a halide promoter.
None of the five Japanese Patent Applications disclose a process for producing acetic acid from an alcohol or a formate ester using a catalyst mixture consisting essentially of rhodium metal atom and lithium iodide with or without methyl iodide.
It can be seen that the prior art contains many disclosures dealing with the catalytic production of acetic acid. The art also discloses the production of other organic carboxylic acids by other methods. One of the disadvantages in many of these reactions is the presence of water with the eventual need to remove it from the desired organic acid product. This removal is both complicated and costly. Other disadvantages often include the simultaneous occurrence of other reactions leading to the formation of by-products, such as, dimethyl acetal, methyl acetate, ethanol etc. These reactions compete with the organic acid production resulting in low conversion rate and selectivity to organic acid.
Many processes employed for the production of organic acids use a catalyst system containing a source of metal atom and a source of halide atom. The alkali metal halides are often mentioned as suitable halide sources, but no distinction is made between any specific one of the alkali metal halides or between any other halogen compound. Nor do any of the references suggest or recognize the synergistic advantage of the use of mixtures of lithium iodide and methyl iodide in conjunction with rhodium catalyst.